Erosion and Landslide Resource for the CCMA Region


•	Sheet	Removal of fairly uniform layer of surface material from the land surface by continuous sheets of runoff water rather than concentrated into channels.
•	Rill	Type of water erosion in which storm runoff is conducted through channels that are narrow and open and less than 0.3 m deep. Rills can develop into gullies if runoff is persistent enough.
•	Gully	Type of water erosion in which storm runoff is conducted through channels that are narrow and open and greater than 0.3 m deep.
•	Tunnel	Hydraulic removal of subsurface soil resulting in formation of underground channels. Can develop into gullies if surface soil collapses.
•	Wind	Movement or bouncing of soil particles across the soil surface occurring when the force of the wind exceeds the resistance of the soil surface.

•	Stream Bank	Removal of soil from the sides of an existing watercourse and deposition of sediment to waterways through loss of riparian vegetation.
The terminology is consistent with the Corangamite Catchment Management Authority’s Land Resource Assessment prepared by The Department of Primary Industries.

The terms susceptibility, hazard and risk are commonly used in day-to-day life with specific reference to risk management. However the terms have different meanings to different people. The concepts of risk management have been adopted as a critical approach in addressing the impacts of erosion and landslides in the CCMA region. In order to achieve a consistency of ideas and understanding, the following definitions of terms have been applied throughout this resource.

•	Susceptibility mapping involves the classification and spatial distribution of the existing and potential threats in the study area. As such it applies to existing (or known) occurrences and to areas of potential occurrences. Susceptibility analysis examines sites of known occurrences, investigates various factors and parameters at those locations and extrapolates them to like areas in the study area in order to predict other potential areas of occurrence.
•	Hazard takes the outcomes from the susceptibility analysis and applies an estimated frequency or annual probability to the threat.
•	Risk is a measure of the likelihood (also referred to as probability) and severity of an adverse effect to health, property or the environment. Risk is often estimated as the product of likelihood and consequence.

Definition of Terms Soil Degradation Processes Mass Wasting or Landslides Soil Erosion Susceptibility, Hazard and Risk Soil Degradation Processes Soil degradation occurs where both natural and human activities cause the soil to become less vigorous or less healthy. The ultimate degradation is the removal or loss of its physical components. Whilst many forms of soil degradation exists such as acidification, salinity, organic depletion, soil structure decline or nutrient depletion, this study specifically deals with erosion (in its many forms) and landslides. Erosion and landslides cause a reduction in the mass and volume of a soil and ultimately lead to modification and/or reduction in the physical extent of the soil ecosystem. The Corangamite Catchment Management Authority (CCMA) Region covers a wide range of land systems. The geological and geomorphological development of these landscapes has resulted in the development of a variety of soils and a diverse range of landscapes. Some of these landscapes and soils are susceptible to land degradation. A breakdown of land degradation issues has been adopted in this study as follows: • Mass Wasting or Landslides • Sheet and Rill Erosion • Gully and Tunnel Erosion Soil degradation processes can be further subdivided into two main groups, natural and anthropogenic. The natural processes are generally episodic and may include climatic, seismic and hydrodynamic including both oceanic and rivers and/or stream sources. The anthropogenic processes can include land use, agricultural activities and the engineered landscape associated with infrastructure, urban development, construction sites, roads and transport arterials.
Mass Wasting or Landslides Landslide terminology adopted in this study is based on the information contained in the following document: “Practice Note Guidelines for Landslide Risk Management 2007” Australian Geomechanics. Volume 42, No.1, March 2007. Produced by Australian Geomechanics Society Landslide Taskforce, Landslide Practice Note Working Group. The term “landslide” denotes the movement of a mass of rock debris or earth down a slope (AGS 2000). The term includes slides, topples and rockfall but does not include ground subsidence or collapse. Classification of landslides is based on a two-term descriptor; the first term describing material type prior to failure and the second term describing the type of movement (AGS 2007, after Varnes 1978). Material types include rock, soil, earth and debris. The five types of kinematicaly distinct movement are: fall, topple, slide, spread and flow. (see figure at right)	Click for larger image


Rockfall	Flow
Top of Page Soil Erosion Soil erosion involves the dislodgement of soil particles, their removal, transport away and eventual deposition in a location remote from the source. Susceptibility to erosion and the rate at which it occurs depends on many factors including land use, geology, geomorphology, climate, soil texture, soil structure, nature and density of vegetation and land management practices. For the purposes of this study, the various forms of soil erosion can be described as follows: